Building contractors in the construction industry, and especially carpenters, are often required to install a large number of fasteners in walls or other reference surfaces. Unless the fastener is self-tapping, or splitting of the surfaces is tolerated, a pilot hole must first be drilled in the reference surface before the fastener is driven therethrough. This is normally achieved by using two electric drills, or by using a single electric drill and firstly using a drill bit fitted to the chuck of the electric drill to drill the pilot hole, and then removing the drill bit and fitting a screw bit to the chuck or removing the chuck altogether and installing a bit holder with fitted screw bit to the drive assembly of the electric drill. This is a time consuming task, especially in circumstances where the contractor must install a large number of fasteners, one after the other, each first requiring a pilot hole. Time is wasted in changing repeatedly between drill bit and screw bit, and the contractor may suffer back strain in bending over frequently to change bits.
U.S. Pat. No. 4,810,916 discloses a rotary power tool having dual heads or bit gripping outputs extending in opposite (or 180 degrees) directions from a central body of the power tool. One output is for a screwdriver bit and the other output is for a drill bit. Both of the outputs are in fixed angular position with reference to the central body. A retractable guard covers the drill bit when not in use. The guard is retracted by the free hand of the user not gripping the central body to expose the drill bit when it is required for use. If, after use, the user forgets or carelessly chooses not to cover the drill bit with the guard by extending it thereover, the drill bit may present a risk of injury to the user as it faces the user's body when the screwdriver bit is being used. The structure of the power tool body (incorporating the handle) is also very different to that of the body of conventional rotary power tools or electric drills.
Australian Patent No. 631,615 discloses a hand held power tool having dual bit gripping outputs which extend in opposite directions from a central body, and which engage respective bits, the outputs being rotatable about 180 degrees to selectively bring either bit to a work station at a forward end of the tool. There is a first manually operated switch for controlling the power supply to the tool, and a second manually operated switch for activating an automated mechanism which turns the head 180 degrees to interchange the positions of the bits. An energy storage means in the form of tensioned springs provides energy for turning of the head, the energy being released by single handed operation of the switches. Whilst enabling the user to keep one hand free when changing the position of the bits, the inclusion of an automated mechanism adds to the structural complexity and weight of the tool.
GB Patent No. 1,357,007 discloses a hand held power tool having a chuck at each end of a rotatable drill head. The drill head is manually turnable through 180 degrees with the use of two hands to allow the chucks to be interchanged at the work site. Because the chuck not being used faces the user's body when the other chuck is in operation at the work site, a guard is provided to protect the user from contacting the chuck, and any bit gripped thereby, not in use. The provision of guards to protect the user from contact with bits that, when not in use, face the user” body, also adds to the structural complexity and weight of the tool.
The present inventor has found that, where installation of a plurality of fasteners requires the drilling of a pilot hole for each fastener, a substantial amount of time can be saved, and less physical exertion is required, if, instead of removing the drill bit from the chuck of the electric drill and then fitting the screw bit to the electric drill, a contractor uses an electric drill having a bit gripping and drive assembly modified so as to operatively support both the drill bit and the screw bit and to allow use of either bit by trigger release and gravity controlled positional adjustment of the bits through 90 degrees that only requires the use of the one hand holding the electric drill. In this way, the need for a guard is eliminated as the bit not in use does not face the user's body. Furthermore, the provision of manual positional adjustment, rather than automated positional adjustment by complex spring loaded or other energy storage means, does not add significantly to the weight of the tool and makes it relatively easier to service and repair. Also, the user may use his other free hand to maintain his hold on a ladder or for other purposes.